The
incidence of diarrheal disease among cruise
ship passengers declined from 29.2 cases per 100,000 passenger days in
1990 to 16.3 per 100,000 passenger days in 2000. In 2002, the Vessel
Sanitation Program of the Centers for Disease Control and Prevention
reported 29 outbreaks (3% or more passengers ill) of acute
gastroenteritis on cruise ships, an increase from 3 the previous year.
This analysis of gastroenteritis on cruise ships, conducted in 2005,
details the increase in outbreak incidence rates during 2001 through
2004. Using Gastrointestinal Illness Surveillance
System data, investigators evaluated incidence rates of gastroenteritis
on cruise ships calling on U.S. ports, carrying 13 or more passengers,
by cruise length and reporting region during the study period. The
investigators also evaluated the association between inspection scores,
and gastroenteritis incidence and the frequency of outbreaks in 2001
through 2004. During the study period, the
background and outbreak-associated incidence rates of passengers with
acute gastroenteritis per cruise were 25.6 and 85, respectively. Acute
gastroenteritis outbreaks per 1000 cruises increased overall from 0.65
in 2001 to 5.46 in 2004; outbreaks increased from 2 in 2001 to a median
of 15 per year in 2002–2004. Median ship inspection scores remained
relatively constant during the study period (median 95 on a 100-point
scale), and were not significantly associated with either
gastroenteritis incidence rates (risk ratio, 1.00; 95% confidence
interval, 0.98–1.02) or outbreak frequency (Spearman’s coefficient,
0.01, p=0.84).
Despite good
performance on environment health sanitation inspections by cruise
ships, the expectation of passenger cases of gastroenteritis on an
average 7-day cruise increased from two cases during 1990–2000 to three
cases during the study period. This increase, likely attributable to
noroviruses, highlights the inability of environmental programs to
fully predict and prevent risk factors common to person-to-person and
fomite spread of disease.

In 1975, the then-Center for
Disease Control (CDC)
established the Vessel Sanitation Program (VSP) to minimize the risk
for diarrheal disease among passengers and crew aboard ships by
assisting the cruise ship industry in developing and implementing
comprehensive environmental health programs. To evaluate the
relationship between cruise ship sanitation scores and diarrheal
disease incidence and outbreaks among cruise ship passengers.
Retrospective cohort study of ship inspection and diarrheal disease
data from 1990 through 2000 from the National Center for Environmental
Health, CDC database, for cruise ships entering the United States.
Yearly trends in number of ships inspected, number of inspections
conducted, inspection scores, and risks of failing inspections; rates
of diarrheal disease among passengers, by inspection year, cruise
duration, incidence of outbreaks, and passing- or failing-score status
of the associated ship. From 1990 through 2000, inspection scores
gradually increased from a median of 89 in 1990 to 93 in 2000
(p<0.001), with an associated statistically significant 21% increase
in likelihood of passing. The total baseline level of diarrhea among
passengers was 2.0 cases per cruise (13243/6485), or 23.6 cases per
100,000 passenger-days (13243/56129096). The latter rate declined
significantly from 29.2 in 1990 to 16.3 in 2000 (p<0.0001).
Diarrheal disease incidence rates among passengers sailing on ships
that passed environmental inspections were significantly lower than
rates among passengers sailing on ships that failed inspections (21.7
vs 30.1; RR = 1.39; 95% CI: 1.31-1.47). Diarrheal disease
outbreak-related illnesses decreased from 4.2 to 3.5 per 100000
passenger-days from 1990-1995 to 1996-2000. Environmental sanitation
inspections conducted among ships sailing into the United States appear
to continue to decrease diarrheal disease rates and outbreaks among
passengers.

This
report describes 5 norovirus-associated gastroenteritis outbreaks that
occurred
during 1 July-2 December 2002
on cruise ships with
foreign itineraries
sailing into ports in the USA.
The cruise
ship outbreaks demonstrate how easily
norovirus can be transmitted from person to person in a closed
environment.